Inflatable bladders have been used in articles of footwear as cushioning within shoe soles and shoe uppers. When positioned within a shoe upper, an inflatable bladder may be used to provide cushioning as well as improve the fit of the article of footwear. In some cases, the bladder may be used instead of conventional lacing to hold the shoe on the foot of the user. Inflatable bladders may also be used under the foot of the wearer to cushion the impact of the foot as it moves through a gait cycle.
Inflatable bladders may be, for example, formed from two sheets of fluid-impervious thermoplastic film that have been sealed together to form an air-tight chamber. For example, U.S. Pat. No. 6,785,985 and U.S. patent application Ser. No. 10/887,927, which are incorporated by reference herein in its entirety, disclose bladders formed from sheets of a light urethane film, a polyester film such as MYLAR®, an ethyl vinyl acetate film or another barrier film. For example, bladders for footwear have been made from a matted polyurethane film commercially available from J. P. Stevens & Co (Easthampton, Mass.) under the product number ST-1880 M2. Two sheets of thermoplastic film are sealed along various weld lines, for example by radio frequency (RF) welding, to form an air-tight inflatable bladder.
However, where weld lines are close together and form a narrow fluid channel within the bladder, air movement through the narrow channels may become restricted causing squeaking with each step taken by the wearer due to tight flow tolerances. Also, the interior surfaces of the bladder may have a tendency to temporarily adhere or stick together, due to static, friction or the nature of the materials.